Ultrasound stethoscope ignores noisy environments

An ultrasound stethoscope, which is immune to interference from background noise, could help medics care for injured soldiers or civilians in very noisy settings, researchers say.

The stethoscope is a useful tool for quickly diagnosing damage to the heart or lungs, which many victims of traumatic injuries can suffer. But they can be difficult to use when background noise reaches about 80 decibels - the same as a busy street. These surrounding sounds can then drown out audio information that is crucial to an accurate diagnosis.

The new "noise-immune" stethoscope works even when background noise reaches 120 decibels - similar to the front row of a rock concert. It was created by Adrianus Houtsma and Ian Curry from the US Army Aeromedical Research Laboratory in Alabama, US, along with John Sewell and William Bernhard from Active Signal Technologies, based in Maryland, US.

The device works by sending a beam of ultrasound into the body, and detecting the reflected signal as it bounces off a patient's internal organs. When the beam bounces of something moving - like a beating heart or a pulsing artery - the Doppler effect causes the frequency to shift.

Frequency shifts

These frequency changes are then converted into sounds that a doctor can hear through headphones. As background noise does not interfere with the high frequency ultrasound, it does not interfere with the signal. The user must, however wear headphones that also block out other sounds. And a gel is needed to conduct sound correctly between the patient and the device.

"I expect this invention to save many lives that otherwise might have been lost," says Houtsma. "It may mean life or death for a seriously injured person."

Specialist training

The noise-immune stethoscope is a clever way to get around background noise, says John Torry, a medical engineer who works at Sussex University, UK. "But it might not be so easy to operate," he warns. "It provides slightly different information to a normal stethoscope and interpreting medical ultrasound information usually needs specialist training."

Wade Allison, a physicist at Oxford University, UK, is also impressed by the idea. "Not enough is known about how sound behaves in the human body," he told New Scientist. "We need more ideas like this."

But he adds that doctors may need a steady hand when using the stethoscope, as any movement will also cause Doppler shifts. "In a helicopter, there will be a lot of things moving," Allison notes, "including the operator of the device".

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A stethoscope that uses ultrasound to detect the movement of the heart or lungs can be used in noisy environments (Image: Adrianus Houtsma)